In the commercial production of powder-form or granular detergents and cleaners a spray drying process is normally used, such as by hot spraying in a tower. The starting material that is spray dried is an aqueous suspension or slurry which contains a high percentage of, or even all, the detergent ingredients. From an economic point of view, it is important that the slurry should contain as high a percentage of detergent ingredients as possible, i.e. as low a percentage as possible of liquid ballast. Accordingly, the smallest possible quantity of water is used for preparing the slurries. However, the concentration is limited by the highest possible viscosity at which the slurry can still be processed, i.e. pumped and sprayed.
An essential ingredient of most detergents and cleaners are anionic surfactants which are generally used as pastelike concentrates in the form of their alkali metal or ammonium salts in the production of the detergent slurry. In the case of .alpha.-sulfo tallow fatty acid methyl ester, for example, the surfactant content of industrial concentrates amounts to approximately 30% by weight. However, pastes of such surfactant having a higher surfactant content can not be processed successfully. U.S. Pat. No. 2,195,187 describes .alpha.-sulfo-fatty acids and their esters as surface-active compounds or surfactants. Also, German Application No. 12 46 718, for example, describes a process for the preparation of this class of compounds.
One peculiar aspect of the rheological behavior of these surfactant concentrates lies in the fact that they react to the addition of water not by a reduction in viscosity, but instead by an increase in viscosity to a gel-like state which presents the processor with additional problems. For example, it is often not easy to redissolve gel lumps once they have formed, and the valves of pumps and containers become blocked.
Various solutions to these problems have been proposed. For example, German Application No. 22 51 405 (corresponding to U.S. Pat. No. 3,893,955) describes the salts of certain carboxylic acids, particularly hydroxy carboxylic acids, as viscosity regulators. According to the teaching of German application No. 23 05 554 (corresponding to U.S. Pat. No. 3,899,448) sulfonated aromatic compounds are suitable for this purpose. German Application No. 23 26 006 (British equivalent No. 1,437,089; Canadian equivalent No. 991,502) discloses sulfates or sulfonates of aliphatic, optionally substituted hydrocarbons as viscosity regulators. The addition of lower alkanols is also mentioned in the cited publications as a means for reducing viscosity. The addition of well known hydrotropes, such as for example cumene sulfonate, or of acidic phosphoric acid esters is mentioned in German application No. 16 17 160 while the addition of polyhydric alcohols and the addition of certain carboxylic acids and/or esters of these compounds is described in EP No. 8060 A (corresponding to U.S. Pat. No. 4,239,641). It is known from EP No. 24 711 A (New Zealand equivalent No. 8,005,342) that sulfates of certain polyalkyl ether glycols can be added to improve the rheological behavior of anionic surfactant concentrates.
Some of the additives mentioned in the literature do not work in all surfactant concentrates, some have to be used in high concentrations, while others, such as lower alkanols, reduce the flash point of the concentrates.